1. Technical Field
The present invention belongs to the field of vaccines against infectious diseases. More particularly, it relates to vaccines against Porcine Reproductive and Respiratory Syndrome (PRRS), a viral disease affecting pigs.
2. Background Information
The Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) is a (+)stranded ssRNA virus belonging to the family of Arteriviridae. The virus exists as two genotypes referred to as “US” and “EU” type which share about 50% sequence homology (Dea S et al. (2000). Arch Virol 145:659-88), and which can be also distinguished by their immunological properties. Most sequencing information on various isolates is based on the structural proteins, namely the envelope protein GP5 which accounts for only ˜4% of the viral genome, while only little is known on the non-structural proteins (nsp).
The nsp2 protein has 1078 amino acids in the EU type prototype Lelystad Virus (LV), and shares only 32% homology with PRRSV-US (Allende R et al. (1999). J Gen Virol 80:307-15). It induces serum antibodies during natural infection (Oleksiewicz M B et al. (2001a). J Virol 75:3277-90, Oleksiewicz M B et al. (2001b). Vet Microbiol 81:109-25), seems to play a crucial role for viral replication (Snijder E J et al. (2001). J Gen Virol 82:985-94, van der Meer Y et al. (1998). J Virol 72:6689-98) and is thought to have species-specific functions (de Vries A A F et al. (1997). Seminars in Virology 8:33-47). The nucleotide sequence coding for the nsp2 amino acid sequence is represented in SEQ ID NO: 2. Length variations in the nsp2 coding region have so far only been described for one US-type isolate (Shen S et al. (2000). Arch Virol 145:871-83) and for EU type strains found in the US (Fang Y et al. Virus Res. 2004 Mar. 15; 100(2):229-35, Ropp S L et al. J Virol. April 2004; 78(7):3684-703.
Isolation of PRRSV and manufacture of vaccines have been described in a number of publications (WO 92/21375, WO 93/06211, WO93/03760, WO 93/07898, WO 96/36356, EP 0 676 467, EP 0 732 340, EP 0 835 930). There is still the need to provide vaccines with improved characteristics, in particular with respect to efficacy and safety.